Such a vehicle-mounted electronic device is installed, for example, in a one box vehicle and is configured such that a rear seat display device displays various content to be viewed from the rear seat.
In recent years, such a vehicle-mounted electronic device has also been required to perform unauthorized content reproduction restriction. As a countermeasure to this, it has been examined to adopt a content protection technology by which, for example, audio output is stopped when unauthorized content reproduction is detected (for example, see the following Patent Literature 1).